Ball grid arrays (BGA) are a relatively new type of surface mount packaging wherein a matrix of solder balls is utilized to provide mechanical and electrical coupling between at least one electronic component and a host printed circuit board (PCB). A representative BGA-to-PCB interface may be formed by first depositing solder paste on selected BGA pads in a grid of BGA pads formed on a mounting surface of a host PCB. An electronic component, which has a corresponding grid of BGA pads formed thereon, is then positioned over the PCB. The electronic component is positioned such that each solder ball resides between and contacts a BGA pad of the electronic component and a BGA pad of the PCB. A reflow process is subsequently performed wherein the assembly is heated (e.g., via an infrared heater) while the electronic component is urged toward the PCB in a controlled manner (e.g., by a robot). As it approaches its melting point, each solder ball deforms and adheres to the bonding surfaces provided on the PCB pads. Each solder ball in the BGA thus forms a mechanical and electrical connection between the host PCB and the electronic component.
The continual demand to decrease the size and weight of electronic components has lead to the development of high density BGAs (also commonly referred to as “fine pitch BGAs”). In such high density BGAs, the outer diameter of each BGA pad provided on the PCB is reduced. This reduction in the size of the PCB BGA pads permits spacing between the pads and other conductive elements (e.g., plated through-hole vias) located on the PCB to be decreased; however, this reduction in the size of the PCB BGA pads also results in a corresponding decrease in the bonding surface area of each BGA pad and, therefore, a decrease in the overall mechanical strength of the BGA-to-PCB interface. In many applications, this decrease in mechanical strength is acceptable and does not negatively impact the reliability of the BGA-to-PCB interface. However, this decrease in mechanical strength may render the BGA-to-PCB interface unsatisfactory for use in certain applications wherein significant mechanical stressors (e.g., high vibratory forces) are routinely experienced, such as deployment within the inverter assembly of an electric or hybrid vehicle.
At least two main approaches have been introduced to increase the mechanical strength of the BGA-to-PCB interface in high density BGAs. In a first approach, the volume between solder balls and under the BGA is filled with an adhesive, such as epoxy glue. The epoxy glue significantly increases the strength of the BGA-to-PCB interface by bonding each solder ball to surrounding components of the PCB (e.g., the PCB BGA pad, the soldermask, etc.). However, the underfilling of the epoxy also adds undesirable cost and complexity to the manufacturing procedure. Furthermore, cracks or fractures may develop during device operation due to a difference in the coefficient of thermal expansion between the epoxy and the BGA package.
The strength of the BGA-to-PCB interface may also be increased by moving the plated through-hole vias into some or all of the PCB BGA pads and such that the vias are no longer located between the BGA pads on the circuit board. Such a via-in-pad approach permits the outer diameter, and thus the area of the bonding surface, of each BGA pad to be increased thereby improving the overall mechanical strength of the BGA-to-PCB interface. However, such a via-in-pad approach also increases the likelihood that solder may weep into the via through-hole during device processing. Although the via through-holes may be plugged with epoxy to prevent such solder weeping, the process of plugging the via through-holes adds considerable cost and complexity to the manufacturing process.
It should thus be appreciated that it would be desirable to provide a high density PCB BGA system that achieves a relatively high mechanical strength. Preferably, embodiments of such a PCB BGA system would be reliable and relatively inexpensive to produce. It would also be desirable for embodiments of such a PCB BGA system to provide an efficient heat dissipation path through the BGA-to-PCB interface. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.